Behavior for wireless transmit/receive unit and mac control elements for lte drx operations

ABSTRACT

A wireless transmit/receive unit (WTRU) stops discontinuous reception (DRX) timers that are running and that are related to uplink and/or downlink transmissions during a DRX time period. The WTRU stops the DRX timers in response to receiving a medium access control (MAC) control element signal from an eNode-B.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.61/036,833 filed on Mar. 14, 2008, which is incorporated by reference asif fully set forth.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

In the Third Generation Partnership Project (3GPP), discontinuousreception (DRX) is used between the network and a User Equipment (UE) tosave the power of the UE. The UE may be configured by a radio resourcecontrol/media access control (RRC/MAC) with a DRX functionality thatallows it to stop monitoring the packet data control channel (PDCCH) fora period of time (i.e., a sleep period). The DRX functionality consistsof a long DRX cycle, a DRX inactivity timer, and a DRX retransmissiontimer. The DRX functionality optionally includes a short DRX cycle and aDRX short cycle timer, which are all defined in the 3GPP specification.The long DRX cycle provides a longer sleep period for the UE than doesthe short DRX cycle.

The active time is defined as the time that the UE is awake. When DRX isconfigured by a higher layer, this includes the on duration, which isthe time that the UE is continuously monitoring the PDCCH while the DRXinactivity timer has not expired, and the time that the UE iscontinuously monitoring the PDCCH while any DRX retransmission timer isrunning.

As shown in FIG. 1, the DRX cycle specifies the periodic repetition ofthe on duration followed by a possible period of inactivity. The DRXinactivity timer specifies the number of consecutive transmission timeintervals (TTIs) during which the UE monitors the PDCCH aftersuccessfully decoding a PDCCH transmission which indicates an initialuplink or downlink user data transmission for the UE. This DRXinactivity timer is restarted if a new PDCCH transmission is detectedwhile the timer is still running. Expiration of the DRX inactivity timerindicates that a particular duration of inactivity has elapsed forreceiving any PDCCH transmission. The DRX retransmission timer specifiesthe maximum number of consecutive TTIs the UE monitors the PDCCH when adownlink retransmission is expected by the UE. The DRX short cycle timerspecifies a number of consecutive TTIs that the UE shall follow theshort DRX cycle after the DRX inactivity timer has expired. The hybridautomatic repeat-request (HARQ) round-trip time (RTT) timer specifiesthe minimum amount of TTIs before a downlink HARQ retransmission isexpected by the UE. The DRX on duration timer specifies a number ofconsecutive PDCCH subframes at the beginning of a DRX cycle andspecifies the number of consecutive TTIs during which the UE monitorsthe PDCCH for possible allocations. The DRX on duration is a part of aDRX cycle.

As mentioned above, the UE may be configured by the RRC/MAC with a DRXfunctionality that allows it to stop monitoring PDCCH during some periodof time. Regardless of whether the UE is monitoring PDCCH, the UEreceives and transmits HARQ feedback when such is expected.

FIG. 2 illustrates an example DRX cycle timing diagram 200, as ademonstration of problems that may arise with interworking of thevarious DRX timers during the selection of a short DRX cycle or a longDRX cycle. As shown in FIG. 2, an initial DRX inactivity timer start 201can occur during any subframe or TTI within the DRX on duration. The DRXinactivity timer duration 202 is fixed. However, due to the uncertaintyof the first start of the first DRX inactivity timer 201, as well as theunknown number of DRX inactivity timer restarts 203 that may berequired, the DRX inactivity timer expiration is uncertain to both theeNode-B and the UE. If the DRX short cycle timer is configured to startwhen the DRX inactivity timer expires, then the new DRX short cycletimer will start at an uncertain subframe or TTI. As a result, theeNode-B does not know with certainty when the short DRX cycle timerstarts and the short DRX cycle may no longer be aligned with the longDRX cycle.

SUMMARY

A method and apparatus is disclosed for selection of DRX short cycle orDRX long cycle, starting a short DRX cycle timer, controllingtermination and expiration of DRX timers, and handling MAC controlelements defined to control these DRX parameters. The method andapparatus are applicable to RRC_Connected mode for both downlink anduplink transmissions.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an example DRX Cycle;

FIG. 2 illustrates an example of uncertainties related to a DRXinactivity timer operation;

FIG. 3 shows an example wireless communication system including aplurality of wireless transmit/receive units (WTRUs) and a base station;

FIG. 4 is a functional block diagram of a WTRU and the base station ofFIG. 3;

FIG. 5 shows method flow chart for selection of short DRX cycle and longDRX cycle when a DRX inactivity timer expires according to a firstembodiment;

FIG. 6 shows a method flow chart for selection of short DRX cycle andlong DRX cycle when a DRX inactivity timer expires according to a secondembodiment; and

FIG. 7 shows a method flow chart for selection of short DRX cycle andlong DRX cycle when a DRX on duration timer expires.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 3 shows a wireless communication system 300 including a pluralityof WTRUs 310, and a base station 320. As shown in FIG. 3, the WTRUs 310are in communication with the base station 320, and the base station 320is in communication with a network 330. Although three WTRUs 310 andbase station 320 are shown in FIG. 3, it should be noted that anycombination of these wireless devices may be included in the wirelesscommunication system 300.

FIG. 4 is a functional block diagram 400 of the WTRU 310 and the basestation 320 of the wireless communication system 300 shown in FIG. 3. Asshown in FIG. 4, the WTRU 310 is in communication with the base station320. In addition to the components that may be found in a typical WTRU,the WTRU 310 includes a processor 415, a receiver 416, a transmitter417, and an antenna 418. The processor 415 is configured to perform themethods disclosed herein for setting DRX timers and selecting DRX cyclelengths during RRC_Connected mode, in conjunction with the DRX timers: aDRX inactivity timer 410, a DRX retransmission timer 411, a DRX shortcycle timer 412, a DRX long cycle timer 413, a DRX on duration timer414, and a HARQ RTT timer 419. The receiver 416 and the transmitter 417are in communication with the processor 415. The antenna 418 is incommunication with both the receiver 416 and the transmitter 417 tofacilitate the transmission and reception of wireless data.

In addition to the components that may be found in a typical basestation, the base station 320 includes a processor 425, a receiver 426,a transmitter 427, and an antenna 428. The processor 425 is configuredto define and send MAC control elements for controlling the WTRU DRXcycles during RRC_Connected mode. The receiver 426 and the transmitter427 are in communication with the processor 425. The antenna 428 is incommunication with both the receiver 426 and the transmitter 427 tofacilitate the transmission and reception of wireless data.

In a first embodiment, the WTRU 310 behavior is defined for operation ofthe DRX short cycle timer 412, the DRX long cycle timer 413, the shortDRX cycle, and the long DRX cycle with respect to expiration of DRXinactivity timer 410. Here, the DRX short cycle timer 412 starts from aknown time boundary, such as a predefined time when the short DRX cycleshould start. The DRX short cycle timer 412 does not start immediatelywhen the DRX inactivity timer expires 410. Instead, the DRX short cycletimer 412 is triggered following expiration of the DRX inactivity timer410, at a subframe or TTI that is a known time boundary for the DRXshort cycle timer 412 to be triggered. In this way, the short DRX cyclecan be easier synchronized with the long DRX cycle.

The following presents several options for the WTRU 310 to deal withdifferent scenarios for the DRX cycle timers.

In a first scenario, a DRX long cycle timer is utilized in addition tothe DRX short cycle timer. The DRX long cycle timer is a parameter thatspecifies the number of consecutive subframe(s) the WTRU 310 shallfollow the long DRX cycle after the DRX Inactivity Timer has expired. Inthis embodiment, both the DRX long cycle timer 413 and the DRX shortcycle timer 412 are both running simultaneously, each timer havingstarted at the beginning of the configured DRX cycle. As such, the DRXshort cycle timer 412 is not triggered by other factors, and starts andexpires autonomously (e.g., irrespective of whether the DRX inactivitytimer 410 expires). The DRX short cycle timer 412 is aligned with thestart of the long DRX cycle (and is a fraction of long DRX cycle) untilthe end of the configured DRX cycle.

FIG. 5 shows a method flowchart 500 for operation of the DRX cycletimers under the first scenario, when the DRX inactivity timer 410expires. At 501, the DRX inactivity timer 410 expires in the downlinksubframe. Then a determination is made as to whether the short DRX cycleis configured at 502. The processor 415 enters the long DRX cycle at 505if the short DRX cycle is not configured. If the short DRX cycle isconfigured, the WTRU processor 415 determines if the DRX short cycletimer 412 has expired at 503. If the DRX short cycle timer 412 has notexpired, then the processor 415 enters the short DRX cycle at 504. Theprocessor 415 enters the long DRX cycle or starts the DRX short cycletimer 412 at 506 if the DRX short cycle timer 412 has expired at 503.Whether to use the long DRX cycle or to start the DRX short cycle timer412 at 506 may be pre-programmed or configured by the eNode-B 320 foreither option during the RRC setup process. If the DRX short cycle timeroption is implemented and it expires in the downlink subframe, then theprocessor 415 uses the long DRX cycle.

In a second scenario, both the DRX long cycle timer 413 and the DRXshort cycle timer 412 are started at the beginning of the configured DRXcycle, and the DRX short cycle timer 412 may be terminated by theeNode-B 320. For example, the eNode-B 320 may send a MAC control element(CE) with an instruction for the WTRU 310 to terminate the DRX shortcycle timer. Once the DRX short cycle timer 412 is terminated, theprocessor 415 will restart the DRX short cycle timer 412 and use theshort DRX cycle.

In a third scenario, the long DRX cycle is used before triggering anyshort DRX cycle. In other words, the long DRX cycle is the default DRXcycle.

The following approach is utilized to achieve synchronization in thesecond and the third scenarios. The elapsed time of the DRX long cycletimer 413 for the WTRU 310 is used to determine whether to enter theshort DRX cycle or the long DRX cycle or to start the DRX short cycletimer 412. It is assumed that one long DRX cycle is N times the lengthof one short DRX cycle (e.g., N(short DRX cycle length)), therelationship can be given as follows:

Long DRX cycle length=N(short DRX cycle length)

where N is an integer.

FIG. 6 shows a method flow chart for the WTRU 310 entering the long DRXcycle or the short DRX cycle in the case of the second or the thirdscenarios. For a current downlink frame, upon the DRX inactivity timer410 expiring at 601, a determination is made at 602 as to whether theshort DRX cycle is configured. If the short DRX cycle is configured, theprocessor 415 compares the elapsed time from the start of the DRX longcycle timer 413 at 603 against the short DRX cycle length. If the DRXlong cycle timer 413 elapsed time is equal to M(short DRX cycle length),where M is an integer and M≦N, then the processor 415 starts the DRXshort cycle timer 412 at 606. Alternatively at 606, the processor 415may enter the long DRX cycle. Whether to use the long DRX cycle or tostart the DRX short cycle timer may be pre-programmed or may beconfigured by the eNode-B 320 for either option during the RRC setupprocess. If at 603, the processor 415 determines the DRX long cycletimer 413 elapsed time is less than M(short DRX cycle length), then theprocessor 415 waits until the elapsed time is equal to M(short DRX cyclelength) at 604, before starting the DRX short cycle timer 412 orentering the long DRX cycle at 606. Alternatively, for DRX long cycletimer 413 elapsed time greater than M(short DRX cycle length) at 603,the processor 415 waits until the subframe or TTI where the DRX longcycle timer 413 elapsed time equals (M+1)(short DRX cycle length), thenstarts the DRX short cycle timer 412 or enters the long DRX cycle at606. The processor 415 may enter the long DRX cycle at 606 withoutstarting DRX short cycle timer 412.

Returning to the initial decision as to whether the short DRX cycle isconfigured at 602, the WTRU enters the long DRX cycle at 607 if theshort DRX cycle is not configured.

In a second embodiment, the WTRU behavior is defined for operation ofthe DRX short cycle timer 412, the DRX long cycle timer 413, the shortDRX cycle, and the long DRX cycle with respect to expiration of the DRXon duration timer 414. FIG. 7 shows a method flow chart 700 for the WTRUprocessor 415 to select the short DRX cycle or the long DRX cycle whenthe DRX on duration timer 414 expires. After the DRX on duration timer414 expires in the downlink subframe at 701, the processor 415determines whether the short DRX cycle is configured at 702. If theshort DRX cycle is configured, then the processor 415 starts the DRXshort cycle timer 412 at 703 and the WTRU processor 415 enters the shortDRX cycle at 704. If the short DRX cycle is not configured at 702, theWTRU processor 415 enters the long DRX cycle at 706.

Alternatively, the processor 415 may start the DRX short cycle timer 412(at 703) at the subframe when elapsed time from the start of currentlong DRX cycle is equal to an integer N times the short DRX cycle length(i.e., N(short DRX cycle length)).

In a variation of this embodiment, the WTRU processor 415 may directlyenter the long DRX cycle upon expiration of the DRX on duration timer414 in the downlink subframe, irrespective of whether the short DRXcycle is configured in 702.

In a third embodiment, a DRX MAC CE is defined to signal the WTRU 310 toterminate any running DRX timers and WTRU behavior is defined forresponding to receiving a DRX MAC CE. In a first scenario for thisembodiment, a DRX command is defined as a MAC CE to signal the WTRU 310to stop the DRX on duration timer 414 and the DRX inactivity timer 410.This is an indication to the WTRU processor 415 that it can stopmonitoring and decoding the PDCCH for initial transmissions for theremainder of the current DRX cycle. In response, the WTRU 310 behaviouris defined as follows.

When a DRX cycle has been configured and the WTRU 310 receives a MAC PDUon a downlink-shared channel (DL-SCH) that contains a DRX CE, the DRX onduration timer 414 and the DRX inactivity timer 410 are stopped duringthe subframe or TTI. If there are no other timers (e.g., a DRXretransmission timer) running when the DRX on duration timer 414 and theDRX inactivity timer 410 are stopped in this subframe or TTI, and if theshort DRX cycle is configured, the processor 415 starts the DRX shortcycle timer 412 and uses the short DRX cycle. If the short DRX cycle isnot configured, the processor 415 enters the long DRX cycle.

As a variation to this embodiment, if the DRX on duration timer 414 isterminated for a predetermined number of consecutive times and no DRXinactivity timer 410 is running, then the WTRU starts the DRX long cycletimer 413.

A MAC control element (CE) may be defined to stop any or all runningtimers related to downlink and uplink transmissions during a DRX cycle.There may be different types of MAC CEs defined to distinguish the stopof any or all running timers related to uplink transmissions anddownlink transmissions during DRX operations. For example, if the WTRU310 receives a downlink related DRX MAC CE, then the WTRU processor 415stops all related timers (e.g., the DRX on duration timer 414, the DRXinactivity timer 410, the DRX retransmission timer 411 and HARQ RTTtimer 419.) The WTRU 310 also suspends all downlink related receptionand flushes the data saved in the HARQ buffer. Conversely, if the WTRU310 receives an uplink related DRX MAC CE, then WTRU processor 415 stopsall timers related to the uplink transmission during the DRX period. TheWTRU 310 also suspends all uplink related reception and flushes the datasaved in the buffer.

There may be several types of DRX MAC CE, or the DRX MAC CE can be usedfor certain purposes to stop DRX timers. By way of example, the DRX MACCE may only force downlink related DRX timers to stop; only force uplinkrelated DRX timers to stop, or force all DRX related timers(downlink/uplink) to stop.

No matter what type of DRX MAC CE is used, when the DRX MAC CE is usedto force the WTRU 310 to re-enter the DRX sleep period as describedabove, the following options are available for the WTRU processor 415 topredict whether to enter a short DRX cycle or a long DRX cycle. In afirst option, the eNode-B 320 transmits a DRX MAC CE signal to the WTRU310. The signal explicitly notifies the WTRU 310 as to whether it shouldenter a short DRX cycle or a long DRX cycle. A one-bit indication in theDRX MAC CE can be used for this explicit signaling. As a second option,the DRX MAC CE only stops the DRX related timers, and then the WTRU 310enters a short DRX cycle. As a third option, the DRX MAC CE only stopsthe DRX related timers, and then the WTRU processor 415 enters a longDRX cycle.

Further, when the uplink related activity timer expires or is stopped,if the short DRX cycle is configured, then the WTRU processor 415 startsthe DRX short cycle timer and uses the short DRX cycle. If the short DRXcycle is not configured, then the WTRU processor 415 uses the long DRXcycle.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral-purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

1. A method implemented by a wireless transmit/receive unit (WTRU) forselecting a discontinuous reception (DRX) cycle type as a short DRXcycle or a long DRX cycle, where the long DRX cycle has a longer sleepperiod than the short DRX cycle, comprising: receiving a downlinktransmission having a plurality of subframes; for each subframe:monitoring the received downlink transmission for a DRX command mediumaccess control (MAC) control element; starting or restarting a DRX shortcycle timer and selecting the short DRX cycle in response to a receivedDRX command MAC control element if the short DRX cycle is configured;selecting the long DRX cycle if the short DRX cycle is not configured;stopping at least one running DRX timer related to uplink transmissionsin response to the MAC CE on the condition that the MAC CE is defined toinstruct the WTRU to stop at least one DRX timer related to uplinktransmissions; and stopping at least one running DRX timer related todownlink transmissions in response to the MAC CE on the condition thatthe MAC CE is defined to instruct the WTRU to force expiration of the atleast one DRX timer related to downlink transmissions.
 2. The method asin claim 1, wherein the at least one running DRX timer is an inactivitytimer specifying a number of consecutive transmission time intervalsduring which the WTRU monitors a control channel and detects a user datatransmission for the WTRU.
 3. The method as in claim 1, wherein the atleast one running DRX timer is an on duration timer specifying a numberof consecutive control channel subframes at the beginning of a DRXcycle.
 4. The method as in claim 1, wherein the at least one running DRXtimer is a retransmission timer specifying a maximum number ofconsecutive transmission time intervals that the WTRU monitors a controlchannel when a downlink retransmission is expected by the WTRU.
 5. Themethod as in claim 1, wherein the at least one running DRX timer is aHARQ retransmission timer specifying a minimum number of subframesbefore a downlink HARQ retransmission is expected by the WTRU.
 6. Awireless transmit/receive unit (WTRU) configured to select adiscontinuous reception (DRX) cycle type as a short DRX cycle or a longDRX cycle, where the long DRX cycle has a longer sleep period than theshort DRX cycle, comprising: a processor configured to receive adownlink transmission having a plurality of subframes; where for eachsubframe, the processor is configured to monitor the received downlinktransmission for a DRX command medium access control (MAC) controlelement (CE); start or restart a DRX short cycle timer and selecting theshort DRX cycle in response to a received DRX command MAC controlelement if the short DRX cycle is configured; select the long DRX cycleif the short DRX cycle is not configured; stop at least one running DRXtimer related to uplink transmissions in response to the MAC CE on thecondition that the MAC CE is defined to instruct the WTRU to stop atleast one DRX timer related to uplink transmissions; and stop at leastone running DRX timer related to downlink transmissions in response tothe MAC CE on the condition that the MAC CE is defined to instruct theWTRU to force expiration of the at least one DRX timer related todownlink transmissions.
 7. The WTRU as in claim 6, wherein the at leastone running DRX timer is an inactivity timer specifying a number ofconsecutive transmission time intervals during which the WTRU monitors acontrol channel and detects a user data transmission for the WTRU. 8.The WTRU as in claim 6, wherein the at least one running DRX timer is anon duration timer specifying a number of consecutive control channelsubframes at the beginning of a DRX cycle.
 9. The WTRU as in claim 6,wherein the at least one running DRX timer is a retransmission timerspecifying a maximum number of consecutive transmission time intervalsthat the WTRU monitors a control channel when a downlink retransmissionis expected by the WTRU.
 10. The WTRU as in claim 6, wherein the atleast one running DRX timer is a HARQ retransmission timer specifying aminimum number of subframes before a downlink HARQ retransmission isexpected by the WTRU.